This invention relates to a power factor controller which reduces power consumption of a motor at reduced loading, and more particularly to a polyphase power factor controller for use with a line voltage of various phases, typically a three phase line.
In the aforementioned parent application there was described an improved power factor controller for an AC induction motor which samples line voltage and current through a motor and decreases power input to the motor in proportion to the detected phase displacement between the current and voltage to thereby provide less power to the motor as it is loaded. The use of such power factor controller provided improved efficiency to an AC induction motor.
In one embodiment described in the aforementioned parent application there is provided a digital power factor controller circuit which developed a pulse signal representative of the phase lag between voltage and current for each cycle. In that embodiment, a fixed clock is utilized which produced output clock signals at a fixed frequency. A control pulse is developed, the width of which is dependent upon the phase lag signal. The clock pulses are then permitted to be combined with the phase lag signal whereby the number of counts of the clock signal will be dependent upon the width of the phase lag pulse. This number is then counted and subsequently utilized as the control for a triac in series with the motor whereby the turn on time of the triac is dependent upon the phase lag signal.
Although such circuit provides a great improvement over prior art circuits, additional circuitry is needed in order to compare the count of the clock signals with reference clock signals and to subsequently convert such value into a suitable signal for use in controlling the triac.
Additionally, when dealing with a polyphase line voltage, various modifications in the circuitry are needed in order to utilize the concepts of the parent application.
Accordingly, although the aforementioned parent application provides numerous novel features, the present invention provides additional improvements over such power factor controller circuits which are now described.